(1) Field of the Invention
The present invention relates to a process for preparing monobasic pyrophosphates. These compounds possess features that are useful in a wide variety of industries including, but not limited to, food processing, pet food processing, and as specialty industrial chemicals.
(2) Description of the Related Art
Acidic pyrophosphate compounds can be prepared by the following type of reaction where sodium is the exemplary metal: 2 NaH2PO4 is heated to form a dibasic pyrophosphate (Na2H2P2O7) and H2O. Thus, it would appear that the associated monobasic pyrophosphate could be prepared by a similar reaction involving NaH2PO4, Phosphoric acid (H3PO4), and heat. This is not the case, however. Different species that are not exclusively pyrophosphate form, reducing the yield and the associated utility, and the resulting mixed material is hard to handle because it melts at ˜150 C and cools to a glassy state.
Monobasic pyrophosphates (of which the sodium form, NaH3P2O7 has been most widely studied) have been prepared by a process wherein glassy sodium polyphosphate is tempered as a fine powder at 100-200 degrees Centigrade in damp air with a water vapour pressure of 10-200 mbar or in a polar solvent in which the phosphate is insoluble, in the presence of a quantity of water sufficient for hydrolysis, until the mass has overwhelmingly been converted to NaH3P2O7. See, AU 2004/47547
(Patent Number 771905) assigned to BK Giulini.
Additionally, DE 10336363 (WO 2005014474) assigned to PEMEAS GMBH discloses a method for producing crystalline pyrophosphates of the Formula 1: MP2O7 by heating a hydrogen phosphate of the Formula II: M (HPO4)2n H2O in a suitable liquid medium, where M is a tetravalent metal of the Group IV a or IV b and n is a number from 0-20, and the resultant compound of Formula 1 has a particle size of 1-1000 nm. Preferably, M is Ti, Zr, Si, Sn, Ge, or Sn, in particular Ti or Zr, and as such these materials are best denoted as tetrabasic. Polyphosphoric acid, phosphorus (V) oxide and orthophosphoric acid or mixtures thereof are preferably used as the liquid medium. The crystalline pyrophosphates of Formula 1 produced according to said method are suitable for use as additives in fuel cells, and for ceramics or as catalysts in organic reactions. It is expected that similar reaction chemistry with different feedstocks would yield monobasic pyrophosphates.
Now, Applicants have discovered a novel process for preparing monobasic pyrophosphate compounds. Moreover, Applicants' process is less time consuming and simpler. For example, the AU 771905 process requires a tempering hold time that is measured in days or weeks. Also, the DE 10336363 process is conducted in a solvent, and requires separate filtration step. Applicants' process does not require the preparation of a glassy melt or a tempering or filtration step. Finally, Applicants' simpler process results in greater yields since all inputs result in usable product.